Gas-supply system and method

ABSTRACT

A gas-supply system includes a gas container filled with gas, a gas flow controller coupled to the gas container, and an operation device electrically connected to the gas flow controller. The gas-supply system further includes a buffer tank coupled to the gas flow controller and configured to receive the gas from the gas container via the gas flow controller. Furthermore, a pressure transducer disposed on the buffer tank and configured to generate a pressure signal to the operation device according to the pressure of the gas in the buffer tank. The operation device is configured to generate a control signal to the gas flow controller according the pressure signal, and the gas flow controller is configured to adjust the flow rate of the gas according to the control signal to keep the pressure of the gas in the buffer tank in a predetermined pressure range.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims the benefit of U.S. Provisional Application No. 61/918,496, filed Dec. 19, 2013, the entirety of which is incorporated by reference herein.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic apparatus. Semiconductor devices are fabricated by various semiconductor processes. However, since semiconductor devices with smaller size and greater performance are in constant demand, some semiconductor processes are improved and modified.

In an epitaxy process of semiconductor manufacturing, a high-pressure liquefied gas, such as HCl and Cl₂, is utilized. Usually, the high-pressure liquefied gas is transmitted to the epitaxy apparatus at a very high pressure, to satisfy the flow rate and pressure requested by the epitaxy apparatus.

In another epitaxy process, a low-pressure liquefied gas is utilized. Due to the characteristics of the low-pressure liquefied gas, the gas cannot be transmitted by high-pressure, and may not satisfy the flow rate and pressure used by the epitaxy apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and related advantages, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view of a gas-supply system and a semiconductor apparatus in accordance with some embodiments of the disclosure.

FIG. 2 is a diagram of flow rate versus delivery pressure of the semiconductor apparatus as shown in FIG. 1 in accordance with some embodiments of the disclosure.

FIG. 3 is a schematic view of a gas-supply system in accordance with some embodiments of the disclosure.

FIG. 4 is a schematic view of a gas flow controller or MFC (mass flow controller) in accordance with some embodiments of the disclosure.

FIG. 5 is a flow chart of a gas-supply method in accordance with some embodiments of the disclosure.

FIG. 6 is a diagram of flow rate versus delivery pressure of the semiconductor apparatus as shown in FIG. 3 in accordance with some embodiments of the disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of the disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are merely examples and are not intended to be limiting. Moreover, the performance of a first process before a second process in the description that follows may include embodiments in which the second process is performed immediately after the first process, and may also include embodiments in which additional processes may be performed between the first and second processes. Various features may be arbitrarily drawn in different scales for simplicity and clarity. Furthermore, the formation of a first feature over or on a second feature in the description may include embodiments in which the first and second features are formed in direct or indirect contact.

FIG. 1 is a schematic view of a gas-supply system 1 a and a semiconductor apparatus 2 in accordance with some embodiments of the disclosure. The gas-supply system 1 a supplies gas to a semiconductor apparatus 2. In some embodiments, the semiconductor apparatus 2 in accordance with some embodiments.

The gas-supply system 1 a includes gas containers 10 and gas regulators 20 a. The gas containers 10 are filled with gas. The gas containers 10 communicate with the semiconductor apparatus 2 via a tube T1, and supply the gas to the semiconductor apparatus 2 via the tube T1. The gas regulators 20 a are disposed on the tube T1. In some embodiments, a number of the valves E1 are disposed on the tube T1. Each of the gas containers 10 is selectively to supply the gas to the semiconductor apparatus 2 via the valves E1. For example, when one of the gas containers 10 is empty, the valve E1 connected to the empty gas container 10 is switched off, and another valve E1 connected to another gas container 10 is switched on.

In some embodiments, the gas containers 10 are high-pressure gas cylinders. The pressure in the gas containers 10 is in a range from about 500 PSIG (Pounds per Square Inch Gauge) to about 2500 PSIG. For example, the pressure in the gas containers 10 is detected by a pressure sensor (not shown), and is about 2000 PSIG. In some embodiments, the gas is a high-pressure liquefied gas, such as CF₄, N₂O, Cl₂, NH₃, HCl, CO₂, HBr, or SF₆. Further, the high-pressure liquefied gas is not liquefied in a low-pressure environment, such as lower than about 100 PSIG. Therefore, the high-pressure liquefied gas released from the gas containers 10 is not liquefied in the tube T1, or in the downstream of the gas regulators 20 a.

In some embodiments, the semiconductor apparatus 2 is an epitaxy apparatus. When the semiconductor apparatus 2 consumes the gas, the gas flows into the semiconductor apparatus 2 from the gas containers 10 due to the pressure in the gas containers 10. The gas regulators 20 a can be adjusted manually to control a delivery pressure in the tube T1.

FIG. 2 is a diagram of flow rate versus delivery pressure of the semiconductor apparatus 2 in FIG. 1 in accordance with some embodiments of the disclosure. The working pressure of the high-pressure liquefied gas utilized by the semiconductor apparatus 2 is in a range of from about 60 PSIG to about 70 PSIG. The flow rate of the gas utilized by the semiconductor apparatus 2 is from about 5 SLPM (Stand Liter per Minute) to about 100 SLPM. Referring to the curve C1, as shown in FIG. 2, the delivery pressure of the high-pressure liquefied gas in the semiconductor apparatus 2 is within a range of from about 60 PSIG to about 70 PSIG. Therefore, the semiconductor apparatus 2 works fine with the high-pressure liquefied gas.

However, in another epitaxy process, the gas is replaced by a low-pressure liquefied gas, and the gas containers 10 are lower-pressure gas cylinders for containing the low-pressure liquefied gas. For example, the working pressure of the gas utilized by the semiconductor apparatus 2 is in a range of from about 5 PSIG to about 7 PSIG, and the flow rate of the gas utilized by the semiconductor apparatus 2 is from about 5 SLPM (Stand Liter per Minute) to about 100 SLPM.

The low-pressure liquefied gas includes ClF₃, BCl₃, SiH₂Cl₂ (Dichlorosilane, DCS), C₄F₆, C₅F₈, HF or WF₆. The low-pressure liquefied gas may be liquefied if the gas pressure exceeds a saturation vapor pressure at gas room temperature. The gas room temperature is in a range from about 20° C. to about 25° C. The low-pressure liquefied gas may be liquefied in a range from about 30 PSIG to about 100 PSIG. Therefore, the pressure in the tube T1 is in a range from about −5 PSIG to about 15 PSIG at the gas room temperature to prevent the low-pressure liquefied gas from being liquefied.

Referring to the curve C2, as shown in FIG. 2, when the flow rate of the low-pressure liquefied gas in the tube T1 is increased from about 0 SLPM to about 4 SLPM, the delivery pressure of the low-pressure liquefied gas in the semiconductor apparatus 2 is quickly decreased from about 6 PSIG to about 0 PSIG. The reason for this situation is that the gas regulator 20 a has a high flow resistance. The flow resistance of the gas regulator 20 a is a result of the gas flowing through a poppet and a diaphragm (not shown) in the gas regulator 20 a. Due to flow resistance, additional flow rate of the gas in the gas regulator 20 a induces additional delivery pressure drop.

In some embodiments, if the delivery pressure is lower than a predetermined working pressure of the semiconductor apparatus 2 at a corresponding flow rate, such as at least 5 SLPM, of the low-pressure liquefied gas, the semiconductor apparatus 2 stops working.

FIG. 3 is a schematic view of a gas-supply system 1 in accordance with some embodiments of the disclosure. The gas-supply system 1 includes gas containers 10, gas flow controllers 20, a buffer tank 30, a pressure transducer 40, and an operation device 50. The gas is transmitted from the gas containers 10, under the flow controllers 20, and via the buffer tank 30 to the semiconductor apparatus 2.

In some embodiments, the gas container 10 is a low pressure liquefied gas cylinder. The pressure in the tube T1 is in a range from about −5 PSIG to about 15 PSIG at the gas room temperature. The gas containers 10 are filled with gas and liquid, and the liquid naturally vaporizes to the gas at the gas room temperature. The gas is the low-pressure liquefied gas, such as DCS.

The gas flow controllers 20 are coupled to the gas containers 10. The gas flow controllers 20 are a mass-flow controller configured to measure and control the flow rate of the gas flowing into the buffer tank 30. The gas flow controllers 20 each adjust the flow rate of the gas to the buffer tank 30. The buffer tank 30 is configured to provide a stable pressure of the gas to the semiconductor apparatus 2. The buffer tank 30 is coupled to the gas flow controllers 20 and receives the gas from the gas container 10 via the gas flow controllers 20. The semiconductor apparatus 2 is coupled to the buffer tank 30 and receives the gas from the buffer tank 30.

In some embodiments, the gas flow controllers 20 are coupled with the gas containers 10 via a tube T2. The buffer tank 30 is coupled with the gas flow controllers 20 via a tube T3. The buffer tank 30 receives the gas from the gas container 10 via the tube T2, the gas flow controller 20, and the tube T3. The semiconductor apparatus 2 is communicated with buffer tank 30 with a tube T4 and receives the gas from the buffer tank 30 via the tube T4.

The pressure transducer 40 is disposed on the buffer tank 30. The pressure transducer 40 detects the pressure in the buffer tank 30 and generates a pressure signal S1 to the operation device 50 according to the pressure of the gas in the buffer tank 30.

The operation device 50 is electrically connected to the gas flow controllers 20 and the pressure transducer 40. In some embodiments, the operation device 50 is a computer. The operation device 50 generates a control signal S2 to the gas flow controllers 20 according to the pressure signal S1, and the gas flow controllers 20 adjust the flow rate of the gas according to the control signal S2.

In some embodiments, the gas-supply system 1 further includes heating devices 60. The heating device 60 heats the corresponding gas containers 10, and keeps the temperature of the gas in the gas container 10 in a range of from about 30° C. to about 45° C. For illustration, the temperature of the gas in the gas container 10 is detected by a thermometer (not shown), and is about 40° C. In some embodiments, the environment temperature is in a range of from about 20° C. to about 24° C., and the ignition temperature of the gas is a range of from about 52° C. to about 58° C. The environment temperature is defined as the temperature around the gas-supply system 1 and the semiconductor apparatus 2. In some embodiments, the environment temperature is about 22° C., and the ignition temperature of the gas is about 55° C.

When the temperature of the gas in the gas containers 10 increases, the pressure in the containers 10 increases. However, a higher temperature may cause the gas to ignite. In some embodiments, the temperature of the gas in the gas containers 10 is limited to being lower than the ignition temperature of the gas.

In some embodiments, the temperature of the gas in the buffer tank 30 is in a range from about 20° C. to about 25° C. For illustration, the temperature of the gas in the buffer tank 30 is detected by a thermometer (not shown) and is about 22° C., substantially equal to the environment temperature. In some embodiments, the pressure in the buffer tank 30 is in a range from about 5 PSIG to 7 PSIG. In such a condition, the gas may not be liquefied in the buffer tank 30 and in the tube T4.

FIG. 4 is a schematic view of a gas flow controller 20 in accordance with some embodiments of the disclosure. The gas flow controller 20 includes a housing 21, a first channel 22, a second channel 23, a flow-rate transducer 24, a control module 25, and a valve mechanism 26. The first channel 22, the second channel 23, the flow-rate transducer 24, the control module 25, and the valve mechanism 26 are disposed in the housing 21. The first channel 22 is coupled to the gas container 10 and the buffer tank 30, as shown in FIG. 3. In some embodiments, the first channel 22 is communicated with the tube T2 and T3.

The first channel 22 has a first section 221 and a second section 222. The cross-sectional area of the first section 221 is greater than the cross-sectional area of the second section 222. The cross-sectional area of the first section 221 is greater than the cross-sectional area of the second channel 23.

The two ends of the second channel 23 are connected to the first section 221 of the first channel 22. The flow-rate transducer 24 is disposed on the second channel 23. The flow-rate transducer 24 is configured to detect the flow rate of the gas in the second channel 23, and generate a measuring signal S3 according to the flow rate of the gas in the second channel 23. In some embodiments, the flow-rate transducer 24 includes a first temperature transducer 241 and a second temperature transducer 242. The first temperature transducer 241 and the second temperature transducer 242 are separated from each other and detect the temperature of the second channel 23 at different locations. When the gas flows in the first channel 22 and the second channel 23, the temperatures detected by the first temperature transducer 241 and the second temperature transducer 242 are different.

The control module 25 is electrically connected to the flow-rate transducer 24, the valve mechanism 26, and the operation device 50 (as shown in FIG. 3). The control module 25 is configured to receive the measuring signal S3.

In some embodiments, the flow rate of the gas can be calculated by the control module 25 according to the difference of the temperatures detected by the first temperature transducer 241 and the second temperature transducer 242. For example, when the gas flows in the first channel 22, the temperature detected by the temperature transducer 241 is about 22.03° C., and the temperature detected by the temperature transducer 242 is about 22.04° C. The difference of the temperatures of the temperature transducer 241 and the temperature transducer 242 is about 0.01° C., which corresponds to the flow rate of the gas.

In addition, when the first channel 22 is blocked by the valve mechanism 26, the gas does not flow through the second section 222 of the first channel 22. The temperatures detected by the first temperature transducer 241 and the second temperature transducer 242 are the same. Therefore, the control module 25 determines that the flow rate of the gas is zero due to the same temperatures being detected by the first temperature transducer 241 and the second temperature transducer 242.

The valve mechanism 26 is disposed on the second section 222 of the first channel 22. The valve mechanism 26 is controlled by the control module 25. The flow rate of the gas is adjusted according to the position of the valve mechanism 26 in the second section 222.

In some embodiments, the valve mechanism 26 includes a piezoelectric element 261. The volume of the piezoelectric element 261 changes according the applied voltage V1 on the piezoelectric element 261. The position of the valve mechanism 26 is adjusted according to the volume of the piezoelectric element 261. The control module 25 applies a corresponding voltage V1 to the piezoelectric element 261 according to the control signal S2, and the volume of the piezoelectric element 261 is adjusted by the voltage V1. For example, when the volume of the piezoelectric element 261 increases, the flow rate of the gas in the first channel 22 decreases.

FIG. 5 is a flow chart of a gas-supply method of the gas-supply system 1 as shown in FIG. 3 in accordance with some embodiments of the disclosure. In step S101, the gas-supply system 1 and the semiconductor apparatus 2 are provided. In the gas-supply system 1, the buffer tank 30 is coupled to the gas container 10 and the semiconductor apparatus 2. The semiconductor apparatus 2 receives the gas from the buffer tank 30.

In step S103, the pressure transducer 40 detects the pressure of the gas in the buffer tank 30, and generates a pressure signal S1 to the operation device 50. In step S105, the operation device 50 generates a control signal S2 according to a pressure signal S1 and a predetermined pressure value.

The operation device 50 controls the gas flow controller 20 to keep the pressure of the gas in the buffer tank 30 in a predetermined pressure range. For example, the predetermined pressure range is in a range of from about 5 PSIG to about 7 PSIG.

The predetermined pressure value is set in the operation device 50, and the pressure signal S1 corresponding to the pressure in the buffer tank 30 includes an active pressure value. If the active pressure value is lower than the predetermined pressure value, the pressure of the gas in the buffer tank 30 is lower than the predetermined pressure range. Then, the operation device 50 generates a control signal S2 to the gas flow controller 20 according to the difference between the active pressure value and the predetermined pressure value.

In step S107, the control module 25 of the gas flow controller 20 adjusts the flow rate of the gas flowing into the buffer tank 30 from the gas container 10 according to the control signal S2. In some embodiments, the flow-rate transducer 24 detects the flow rate of the gas flowing into the buffer tank 30 and generates a measuring signal S3 to the control module 25. The control module 25 of the gas flow controller 20 adjusts the flow rate of the gas flowing into the buffer tank 30 from the gas container 10 according to the control signal S2 and the measuring signal S3. After the gas flows into the buffer tank 30, the pressure in the buffer tank 30 gradually rises to the predetermined pressure range. In general, if the active pressure value is lower than the predetermined pressure value, the flow rate of the gas flowing into the buffer tank 30 increases.

If the pressure of the gas in the buffer tank 30 is in a predetermined pressure range, the operation device 50 continually fine tunes the flow rate of the gas flowing into the buffer tank 30 to keep the pressure of the buffer tank 30 at about the predetermined pressure value. If the pressure of the gas in the buffer tank 30 is higher than the predetermined pressure range, the flow rate of the gas flowing into the buffer tank 30 is set to zero or substantially zero. Therefore, the gas flow controller 20 controls the valve mechanism 26 to close the second section 222 of the first channel 22 to block the gas flowing.

When the semiconductor apparatus 2 consumes the gas, the gas flows from the buffer tank 30. In general, the semiconductor apparatus 2 does not continually consume the gas, and the quantity of the gas consumed by the semiconductor apparatus 2 depends on different semiconductor processes. As a result, the pressure in the buffer tank 30 is not constant. Therefore, by the gas-supply system 1 and the gas-supply method, the pressure in the buffer tank 30 can be kept in the predetermined pressure range.

Further, in some embodiments, the volume of the buffer tank 30 is at least two times greater than the volume of the gas container 10. Since the gas transmitted from the buffer tank 30 to the semiconductor apparatus 2 does not pass through any gas regulator, the flow resistance of the gas flowing to the semiconductor apparatus 2 is lower. Therefore, although the flow rate of the gas consumed by the semiconductor apparatus 2 changes, the delivery pressure and the flow rate of the gas applied to the semiconductor apparatus 2 satisfies the requirements of the semiconductor apparatus 2.

FIG. 6 is a diagram of flow rate versus delivery pressure of the semiconductor apparatus 1 as shown in FIG. 3 in accordance with some embodiments of the disclosure. The flow rate of the lower pressure liquefied gas utilized by the semiconductor apparatus 2 is from 10 SLPM to 100 SLPM. The working pressure of the gas utilized by the semiconductor apparatus 2 is in a range from about 5 PSIG to about 7 PSIG. Referring to the curve C3, as shown in FIG. 6, the delivery pressure of the low-pressure liquefied gas in the semiconductor apparatus 2 is within the working pressure. Therefore, the semiconductor apparatus 2 works fine with the low-pressure liquefied gas.

Some embodiments for a gas-supply system are provided. The gas-supply system keeps the pressure of a gas being transferred to semiconductor apparatus in a predetermined pressure range. Further, the flow rate and pressure of low-pressure liquefied gas utilized by the semiconductor apparatus is satisfied by the gas-supply system.

In some embodiments, a gas-supply system is provided. The gas-supply system includes a gas container filled with gas, a gas flow controller coupled to the gas container, and an operation device electrically connected to the gas flow controller. The gas-supply system further includes a buffer tank coupled to the gas flow controller and receives the gas from the gas container via the gas flow controller. The gas-supply system also includes a pressure transducer disposed on the buffer tank and is configured to generate a pressure signal to the operation device according to the pressure of the gas in the buffer tank. The operation device is configured to generate a control signal to the gas flow controller according to the pressure signal, and the gas flow controller is configured to adjust a flow rate of the gas according to the control signal to keep the pressure of the gas in the buffer tank within a predetermined pressure range.

In some embodiments, a gas-supply system is provided. The gas-supply system includes a gas container filled with gas and a gas flow controller coupled with the gas container via a first tube. The gas-supply system also includes a buffer tank coupled with the gas flow controller via a second tube and configured to receive the gas from the gas container. The gas-supply system further includes a pressure transducer disposed on the buffer tank and configured to generate a pressure signal according to a pressure of the gas in the buffer tank. The gas-supply system further includes an operation device receiving the pressure signal and configured to generate a control signal to the gas flow controller according the pressure signal. The gas flow controller is configured to adjust the flow rate of the gas according to the control signal to keep the pressure of the gas in the buffer tank within a predetermined pressure range. The semiconductor apparatus communicates with the gas container with a second tube and is configured to receive the gas from the buffer tank via the second tube.

In some embodiments, a gas-supply method is provided. The method includes detecting pressure of a gas in a buffer tank coupled to a gas container and generating a pressure signal. The method further includes generating a control signal according the pressure signal and a predetermined pressure value. The method further includes adjusting a flow rate of a gas flowing into the buffer tank from the gas container according to the control signal, and receiving the gas from the buffer tank.

Although embodiments of the present disclosure and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims. For example, it will be readily understood by those of ordinary skill in the art that many of the features, functions, processes, and materials described herein may be varied while remaining within the scope of the present disclosure. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. z What is claimed is: 

1. A gas-supply system, comprising: a gas container filled with gas; a gas flow controller coupled to the gas container; an operation device electrically connected to the gas flow controller; a buffer tank, coupled to the gas flow controller and configured to receive the gas from the gas container via the gas flow controller; a pressure transducer, disposed on the buffer tank and configured to generate a pressure signal to the operation device according to the pressure of the gas in the buffer tank, wherein the operation device is configured to generate a control signal to the gas flow controller according to the pressure signal, and the gas flow controller is configured to adjust a flow rate of the gas according to the control signal to keep the pressure of the gas in the buffer tank within a predetermined pressure range.
 2. The gas-supply system as claimed in claim 1, wherein a semiconductor apparatus is coupled to the buffer tank and is configured to receive the gas from the buffer tank.
 3. The gas-supply system as claimed in claim 1, wherein the gas flow controller comprises: a first channel coupled to the gas container and the buffer tank; and a valve mechanism, disposed on the first channel and controlled by a control module, wherein the flow rate of the gas is adjusted according to a position of the valve mechanism in the first channel.
 4. The gas-supply system as claimed in claim 3, wherein the valve mechanism comprises a piezoelectric element, a volume of the piezoelectric element is adjusted by a control module, and the position of the valve mechanism is adjusted according to the volume of the piezoelectric element.
 5. The gas-supply system as claimed in claim 1, wherein the gas flow controller comprises: a first channel coupled to the gas container and the buffer tank; a second channel having two ends connected to the first channel; and a flow-rate transducer, disposed on the second channel and electrically connected to a control module.
 6. The gas-supply system as claimed in claim 1, wherein the gas comprises ClF₃, BCl₃, SiH₂Cl₂, C₄F₆, C₅F₈, HF or WF₆.
 7. The gas-supply system as claimed in claim 1, wherein the pressure in the gas container is in a range from about 9 PSIG to about 30 PSIG, and the temperature in the gas container is in a range from about 35° C. to about 45° C.
 8. The gas-supply system as claimed in claim 1, wherein the predetermined pressure range is from about 5 PSIG to about 7 PSIG, and the temperature in the buffer tank is in a range from about 20° C. to about 25° C.
 9. A gas-supply system, comprising: a gas container filled with gas; a gas flow controller coupled with the gas container via a first tube; a buffer tank, coupled with the gas flow controller via a second tube and configured to receive the gas from the gas container; a pressure transducer, disposed on the buffer tank and configured to generate a pressure signal according to the pressure of the gas in the buffer tank; and an operation device, configured to receive the pressure signal and to generate a control signal to the gas flow controller according to the pressure signal, wherein the gas flow controller is configured to adjust the flow rate of the gas according to the control signal to keep the pressure of the gas in the buffer tank within a predetermined pressure range, and wherein a semiconductor apparatus is communicated with the gas container with a second tube and is configured to receive the gas from the buffer tank via the second tube.
 10. The gas-supply system as claimed in claim 9, wherein the gas flow controller comprises: a first channel communicated with the first tube; and a valve mechanism, disposed on the first channel and controlled by the operation device, wherein the flow rate of the gas is configured to be adjusted according to a position of the valve mechanism in the first channel.
 11. The gas-supply system as claimed in claim 10, wherein the valve mechanism comprises a piezoelectric element, the volume of the piezoelectric element is configured to be adjusted by the operation device, and the position of the valve mechanism is configured to be adjusted according to the volume of the piezoelectric element.
 12. The gas-supply system as claimed in claim 9, wherein the gas flow controller comprises: a first channel coupled to the gas container and the buffer tank; a second channel having two ends respectively connected to the first channel; and a flow-rate transducer, disposed on the second channel and electrically connected to the operation device.
 13. The gas-supply system as claimed in claim 9, wherein the gas comprises ClF₃, BCl₃, SiH₂Cl₂, C₄F₆, C₅F₈, HF or WF₆.
 14. The gas-supply system as claimed in claim 9, wherein the pressure in the gas container is in a range from about 9 PSIG to about 30 PSIG, and the temperature in the gas container is in a range from about 35° C. to about 45° C.
 15. The gas-supply system as claimed in claim 9, wherein the predetermined pressure range is from about 5 PSIG to about 7 PSIG, and the temperature in the buffer tank is in a range from about 20° C. to about 25° C.
 16. A gas-supply method, comprising: detecting pressure of a gas in a buffer tank coupled to a gas container, and generating a pressure signal; generating a control signal according to the pressure signal and a predetermined pressure value; adjusting a flow rate of the gas flowing into the buffer tank from the gas container according to the control signal; and receiving the gas from the buffer tank.
 17. The gas-supply method as claimed in claim 16, further comprising detecting the flow rate of the gas flowing into the buffer tank, generating a measuring signal, and adjusting the flow rate of the gas flowing into the buffer tank from the gas container according to the control signal and the measuring signal.
 18. The gas-supply method as claimed in claim 16, wherein when the pressure of a gas in the buffer tank is in a predetermined pressure range, continually adjusting the flow rate of the gas flowing into the buffer tank to keep the pressure of the buffer tank at about the predetermined pressure value.
 19. The gas-supply method as claimed in claim 16, wherein the pressure in the gas container is in a range from about 9 PSIG to about 30 PSIG.
 20. The gas-supply method as claimed in claim 16, wherein the gas comprises ClF₃, BCl₃, SiH₂Cl₂, C₄F₆, C₅F₈, HF or WF₆. 